1. Field of the Invention
The present invention generally relates to an automobile bodyshell and, more particularly, to a bodyshell frame structure employed therein although not limited thereto.
2. Description of the Prior Art
The frame structure of the type referred to above is used for, for example, side center pillars of the automobile bodyshell. As is well know to those skilled in the art, the side center pillar comprises elongated outer and inner panels welded together along their side flanges to define a hollow of a closed- box section. At least a portion of, the side center pillar where a strength and a rigidity are particularly required, a reinforcement or intermediate panel is interposed between the outer and inner panels. In this type of the frame structure, in order to increase the strength, rigidity and impact energy absorption, various attempts are employed, for example, to employ panels of an increased thickness and/or additional reinforcements,
The Japanese Laid-open Utility Model Publication No. 1-125278 discloses the use of the frame structure of the type discussed above for each of side front pillars of the automobile bodyshell. According to this publication, each side front pillar includes an upper pillar section and a lower pillar section connected at one end with the upper pillar section. Each of the upper and lower pillar sections is comprised of outer and inner panels welded together to define a hollow of a generally closed-box section. However, at a joint between the upper and lower pillar sections, a brace is provided so as to intervene between the upper and lower panels, thereby dividing the hollow of the frame structure into closed outer and inner volumes.
To suppress transmission of vibratory noises to a passengers"" compartment and also to increase the absorption of energies generated in the event of an automobile collision, the publication referred to above discloses the use of an expandable filling material such as, for example, an expandable urethane resin, which fills up completely within the hollow in an upper region of the upper pillar section and, also fills up partially within the hollow in a lower region of the upper pillar section and an upper region of the lower pillar section, that is, only within the closed outer volume delimited between the outer panel and the brace.
Also, according to the above referenced publication, the expandable filling material is injected externally into the hollow in the frame structure by means of a filling gun and expands to fill up the requisite hollow as it is injected thereinto.
Considering that in recent years demand for increase of the mileage of an automobile is pressing, the automobile bodyshell has to be reduced in weight to meet the demand. However, the use of the panels and/or reinforcements of an increased thickness is ineffective to reduce the weight of the automobile bodyshell and also to increase both the mileage and the safety against automobile collision.
Accordingly, the use may be contemplated of the filler such as, for example, a lightweight expandable urethane resin within the hollow of the frame structure so that not only can increase of the weight of the automobile bodyshell be minimized, but also the safety factor against automobile collision can be increased.
The filler made of the expandable urethane resin has a high capability of deforming to a certain extent when a load acts thereon as a result of automobile collision and, accordingly, the filler employed in the form of the expandable urethane resin has such a problem that since an impact load will hardly be transmitted from the point of application thereof in all directions outwardly towards the surroundings through the panels with the frame structure consequently considerably deformed at a local portion adjacent the point of application of the impact load, the energy absorption of the frame structure cannot be increased satisfactorily. Although in terms of the lightweight feature the filler is preferably disposed within a portion of the cross-section of the hollow of the frame structure, not within the entire cross-section of the hollow of the frame structure, the disposition of the filler having a high capability of deforming such as described above within a portion of the cross-section of the hollow of the frame structure is ineffective to increase the energy absorbing power even though effective to reduce the vibrations and noises.
Accordingly, the present invention has been devised to provide an improved automobile bodyshell frame structure, wherein characteristics of material for the filler are carefully chosen to enable the automobile bodyshell to employ a minimized amount of the filler to accomplish the reduction in weight of the automobile bodyshell and also to increase the safety factor against automobile collision.
To accomplish this and other objects and features of the present invention, there is in accordance with the present invention provided an automobile bodyshell frame structure including a generally elongated first panel member, and a generally elongated second panel member having opposite side edge portions connected to the first panel member to define a hollow between the first and second panel members. A filler is disposed within a portion of a cross-section of the hollow between the first and second panel members. This filler is provided on an inner surface of one of the first and second panel members and has an average compressive strength equal to or greater than 4 MPa and/or a maximum bending strength equal to or greater than 10 MPa.
According to the; present invention, the filler is disposed on a portion (a buckling portion) of the panel members which will be deformed to buckle inwardly of the frame structure when an impact load is applied thereto and, therefore, a force acting locally on that portion can be dispersed outwardly through the filler. Accordingly, it is possible to allow that portion of the panel member to effectively absorb impact energies by suppressing any possible bending of that portion and facilitating bending of that portion.
As hereinabove described, the filler has an average compressive strength, as defined later, which is equal to or greater than 4 MPa and/or a maximum bending strength equal to or greater than 10 MPa. This is because, although the energy absorption of the frame structure will increase with increase of the average compressive strength or the maximum bending strength of the filler, the extent of increase, of the energy absorption will saturate if the average compressive strength or the maximum bending strength exceeds 4 MPa or 10 MPa, respectively.
In other words, if the average compressive strength is equal to or greater than 4 MPa, a localized deformation of the frame structure which will lead to collapse of the frame structure can advantageously be minimized. Also, if the maximum bending strength is equal to or greater than 10 MPa, any possible cracking of the filler can advantageously be suppressed to thereby suppress a brittle fracture of the frame structure to a maximum possible extent even though the frame structure is considerably deformed locally. Consequently, if the filler satisfying one or both of the characteristics discussed above is employed, the energy absorption about equal to the maximum value can be obtained and, even though the filler is disposed partially within the frame structure, the safety factor against collision can advantageously increased.
Accordingly, the present invention does not require the use of panel members having an increased thickness for increasing the energy absorption and suffices to use the lightweight filler such as, for example, an expandable filling material made of epoxy resin in particular to accomplish reduction in weight of the automobile bodyshell and to increase the mileage.
In another aspect of the present invention, there is also provided an automobile bodyshell frame structure, which includes a generally elongated first panel member, a generally elongated second panel member having opposite side edge portions connected to the first panel member to define a hollow between the first and second panel members, and an intermediate panel member interposed between the first and second panel members so as to divide the hollow into a first closed volume adjacent the first panel member and a second closed volume adjacent the second panel member. Upper and lower dividing elements are positioned on one of opposite surfaces of the intermediate panel member adjacent the first closed volume and spaced a distance from each other in a direction lengthwise of the frame structure, each of said dividing elements defining a respective gap between it and the first panel member. The filler is expanded to fill up a portion of the first closed volume that is delimited between the upper and lower dividing elements with end portions of the filler filling up the gaps between the upper and lower dividing elements and the first panel member. This filler when not expanded yet being retained in that portion of the first closed volume delimited between the upper and lower dividing elements.
In a further aspect of the present invention, there is also provided an automobile bodyshell frame structure, which includes a generally elongated first panel member, a generally elongated second panel member having opposite side edge portions connected to the first panel member to define a hollow between the first and second panel members, and an intermediate panel member interposed between the first and second panel members so as to divide the hollow into a first closed volume adjacent the first panel member and a second closed volume adjacent the second panel member. A first filler is expanded to fill up at least a portion of the first closed volume and having ends opposite to each other, and a second filler expanded within that portion of the first closed volume and held in abutment with each of the opposite ends of the first filler.